Mufti (Mufty - spelling?) Day

When I was but a young thing starting my working career, a 'new fad' came in called casual days. They were Fridays and you could come to work in your jeans, etc.

Then the name changed somewhere along the line to Mufti (and as you can see I really don't know how to spell that) Day and we had to pay $1 for the privilege.

I dislike the term intensely (not cos I had to pay $1 - I think that went to either charity or our co. social club, which is OK), but because I think it was yet another Americanism that crept into our language. Nothing personal to all you Americans out there, but hey, we're not American, and TV has a lot to answer for in that it seems to be evolving our own language into yours in a rather hurried way. And I guess I'm just a boring old 'you know what', cos I kinda like the way we spoke when I grew up. (Says she using the term 'kinda' - ah, there seems to be no escape!)

Anyway, is 'Mufti' an American term, and is it an acronomym, or an actual word, and where did it come from and when.